Water-swellable smectite clays have a great number of industrial uses that rely upon the ability of the clay to absorb many times its weight in water. Such water-swellable clays, such as sodium bentonite, however, lose much of their absorbency if the water absorbed is contaminated with water-soluble metal salts of alkali metals or alkaline earth metals, particularly the sulfate or halide salts, such as sodium chloride, magnesium chloride, calcium bromide, calcium chloride, potassium chloride, salt-containing body fluids and the like. Some bentonite clays, such as the blue bentonites disclosed in Clem U.S. Pat. No. 2,672,442, have required the uptake of calcium ions to provide acceptable water swellability and colloidal properties for industrial acceptance. The process of the present invention surprisingly provides bentonite clays, especially calcium bentonite and highly water-swellable sodium bentonite clays, with the sustained ability to absorb contaminated water and/or adsorb contaminants from the contaminated water.
The preferred smectite clays useful as starting materials in accordance with the present invention are non-blue sodium bentonites (green to greenish yellow to yellow to cream colored) that have industrially acceptable water swellability and colloidal properties and have a Fe.sup.+3 /Fe.sup.+2 ratio greater than 1, preferably at least 3, and most preferably in the range of about 5 to about 15. However, the process and product of the process of the present invention are useful to improve one or more characteristics, particularly contaminated water absorbency or adsorbency, of any smectite clay, particularly the highly water-swellable sodium bentonites for water absorbency, calcium bentonites for contaminant adsorbence, and blue bentonites, as will become more apparent from the data of the examples. Some of these industrial uses for the treated smectite clays of the present invention, where once dried clays, e.g., sodium bentonite, have their absorbency or contaminant adsorbency adversely affected upon contact with contaminated water, are described as follows.
Clem U.S. Pat. No. 4,021,402 discloses combining bentonite clay with a water-soluble polymer and a dispersing agent to enhance the absorption of salt-contaminated water. Alexander U.S. Pat. Nos. 4,613,542 and 4,624,982 disclose slurrying a water-swellable clay and a water-soluble anionic polymer in water to inhibit the swelling of the water-swellable clay for easier impregnation of a water-penetrable article with the clay slurry. Subsequent heating of the impregnated article breaks down the polymer to revert the clay to water-swellable. Slurrying of the clay in accordance with U.S. Pat. Nos. 4,613,542 and 4,624,982 completely hydrates the clay to a water content of at least 150%, based on the dry weight of the clay, and temporarily inhibits the water-swellability of the clay. This complete rewetting of the clay to such a high water content would not be useful in accordance with the present invention since the subsequent redrying step would be extremely costly and would impregnate the clay with a polymer solution that would be too dilute to achieve the advantages disclosed herein.